PSK21 / SlowPSK User Guide
Contents
1. loss of 2 dB 50 birdies within 1 kHz of each 6 times the signal energy also cause a loss of 2 dB 2 8 2 Block Error Rates of SlowPSK The only difference between PSK21 and SlowPSK is the stretching factor in time The program allows all stretching factors with prime factors less than 8 Useful factors are factor transmission period minutes gain over PSK21 dB 1 1 this is PSK21 0 6 5 7 8 18 15 12 6 36 30 15 6 72 60 18 6 currently not available The block error rates of the different SlowPSKs are derived from Figure by shifting the abscissa by the corresponding gain values The SNR for 50 correct decode no or very slow fading are 1 min 30 dB 5 min 38 dB 15 min 43 dB 30 min 46 dB 3 The SlowPSK Graphical User Interface The Graphical User Interface is shown in Figure 2 The different parts of the GUI are exlained here top down and right left 3 1 The Decoder Window address sender received information 16 24 0 05 0 10 30 dB CQ de sm2cew 16 26 0 05 0 10 30 dB CQ de SM2CEW 16 28 0 05 0 00 31 dB DJ5HG de SM2CEW rep w 16 30 0 05 0 00 30 dB DI5HG de smM2cew RRR The upper half of the GUI figure displays the decoded messages including some meta data Lines belonging to a QSO are printed in red color The window scrolls when the lower line is reached Figure 2 shows a completed simulated QSO with 1 min period at the stage of sending TNX 73 A single left click on a text pastes the lin2. of their contents False decodes of the types CQ de CALLSIGN or QRZ de CALLSIGN can occur 99 9 of them violate the syntax of amateur callsigns The plausibility check usually prevents their display The remaining probability of such false decodes is less than one per 1000 years of continuous operation Strong birdies can lead to the all zeros codeword which is decoded to OSTE SAAL TTIT I This message is forbidden by the program and never displayed False decodes of the type mycall de falsecall with a correct MyCall but false calling call with or without report also can occur An automatic reply then starts a QSO with an alien It will stuck at your reply and never lead to a confirmed QSO The remaining probability of such an occurance is very low Nevertheless you should set the parameters StopTX and StopQSO appropriately to limit such wasted operation 10 2 Fatal False Decodes A fatal decode is a decode which leads to a confirmed but invalid QSO Such false decodes in principle can occur but it hardly should happen while the universe exists 12 Fading 44 5 10 15 20 25 30 35 40 45 time s 1 period Figure 5 Example for fast fading The upper figure shows the real part blue and the imaginary part red of the signal The very fast phase changes are from the modulation 996 bits The lower figure shows the amplitude of the signal SlowPSK can decode this but at a loss of 4 dB SlowPSK
3. the system you use Usually it is something like your private folder documents MATLAB SlowPSK The path to some files are printed into the DOS window at program start 8 1 SlowPSK exe This is the SlowPSK program to be executed on your computer At it s first start it will be unpacked internally which may take a while please be patient 8 2 decodedtext txt This text file prints all messages which are decoded by the SlowPSK program in chronological order The line format is as follows time At Af SNR address de call report locator QSO no PWR ANT PS T365 42 00 O2500 3 0 dBi DJ5HG de SM2CEW rep RW KP15CR 1233 200W 18dB time isin UTC At is the time offset of the decoded block Af is the offset of the decoded signal to the nominal carrier frequency 1000 Hz The SNR is derived from the reconstructed block It heavily depends on the quality of the phase recovery The received report consists of a possible R and one of the letters WML which stand for weak medium and large 8 3 log txt SlowPSK automatically gererates a logfile with lines of the following format startconnect conf stop callsign rptsent sent rptrcvd rcvd locatr pwr ant distance 14 22 14 25 14 29 14 30 GW4WND M RW 136 I082KM 500W 15dB 932km 8 4 SlowPSK_parameters mat This is used to save the actual parameters If you delete this file SlowPSK will start using the default settings If SlowPSK does not start please delete this file or rename it
4. uses Phase Shift Keying as it s modulation The demodulation requires a phase recovery This phase recovery is possible only when the phase changes caused by the radio channel are much slower than those made by the PSK itself The number of fading minima within one period of SlowPSK may roughly be 10 medium fading The loss of sensitivity is about 4 dB if the Rayleigh fading has 20 minima fast fading see Figure 5 If the fading is even faster then incoherent communication modes are better 13 Simulation The simulation mode of SlowPSK is activated by entering some value for the SNR If the SNR is not empty the specified noise in 2500 Hz bandwidth is added to the TX signal If fading is specified other than none then the fading is generated prior to the noise addition A frequency offset can be specified too The selected line to be sent in simulation mode is colored in pink Two computers can communicate via crossed audiocables The callsigns used on both computers must be different 14 Recommended Operation FreqOffset ON A double click on a decoded CQ then applies the observed frequency offset of the other station automatically to the own station which leads to zero beat The own FreqTol parameter is set to 2 or lower The CQ caller can run with this FreqTol value from the first FreqTol must be set with care It is less critical on VHF But on HF QRM dominates and must be made inert by a FreqTol as small as possible If you set
5. FreqTol manually do not forget to increase FreqTol after the QSO FreqTol 20 seems to be a good value on HF If a station is sleeping in AutoMode reply then the caller does not know it s QRG accurately The sleeping station should run with FreqTol 50 The caller can correct his QRG when a reply was decoded Fading must be set appropriately Usually medium fading normally is sufficient on HF but sometimes fast is adequate NoiseBl should be set on HF On VHF the setting depends on the local conditions BirddieBI should be set on HF On VHF the setting depends on the local conditions The PC clock must be set at a precision of about 2 seconds Transceiver Bandwidth can be reduced such that the audio range 1000 FreqTol 1000 FreqTol Hz is in the passband This can considerably decrease the dynamic the soundcard has to deal with In case of pulse like QRM a large bandwidth may be better because the NoiseBlanker then can eliminate the pulses more accurate If the transceiver only allowes to use narrow bandwidth filters in SSB mode with center frequency 1500 Hz the Carrier 1500 may be selected Then the dial frequencies must be set 500 Zh lower TX Power must be limited to the value used in SSB mode Never drive full power with a transistor PA USB should be used normally But LSB also is possible without loss of sensitivity The dial then must be set exactly 2 kHz higher For example 14068 kHz used on USB will appear on 14070 L
6. Klaus von der Heide 1 Introduction SlowPSK is a very sensitive digital mode for weak signals It operates with fixed RX TX periods of 1 5 15 or 30 minutes With a 1 minute period 48 seconds of transmission a rate of 50 correct decodes is reached at 30 7 dB The disadvantage of PSK is that it rapidly degrades in case of fast phase changes by fading SlowPSK with a period of 1 minute also is called PSK21 2 Properties of the SlowPSK Mode 2 1 Demands 1 SlowPSK needs very stable frequencies of TX and RX with a frequency drift less than 2 Hz within the selected period 2 The errors of the samplerate 8000 for sound input and sound output must be determined such that the samplerates are known at an accuracy of 1 Hz 2 2 Modulation SlowPSK uses binary Phase Shift Keying at rates of 125 6 p bits s with p being the stretching factor p 1 6 18 36 for the periods of 1 5 15 30 minutes So the fastest has 20 833 bits s which justifies it s name PSK21 The pulse shape is a sinc function The result is a minimum energy modulation not a constant amplitude modulation 2 3 Signal Spectrum As a consequence of the sinc pulse the spectrum of the transmitted signal has a rectangular shape with a total bandwidth equal to the bit rate 2 4 Code Words SlowPSK transmits binary blocks of 996 bits The length of the transmissions is p 996 6 125 s 2 5 Synchronization One on the main problems of amateur weak signal communicat
7. SB The procedure concerning QSY by the df value mentioned above needs inverted correction in this case df 27 8 gt QSY 28 Hz down instead of up SlowPSK can decode saved audiorecords Please note 1 The basic parameter samplerate must be normal If you use the option 48000 the records are saved with 8000 samples of 8 bits mono the same as in the normal case of 8000 samples s 2 The basic parameter carrier normal 1500 should be the same as that of the recording 3 The actual parameters FreqTol Fading NB BB must be adequate to the saved file You can try to adapt these parameters 4 Differences between the original decoding and the decoding of the saved file may be caused by different parameter settings but also by the compression to only 8 bits per sample in the record 5 General messages CQ QRZ QST will always decode 6 QSO messages will only decode if ToCall is set to the callsign of that QSO and if AutoMode is set to manual 7 Decodes of saved files are displayed in dark green color 8 Except from the displayed color there is no difference to real time decodes It is therefore not a good idea to decode files while an actual QSO is in progress The displayed times may be corrupted and the AutoMode also reacts on the decodes of stored files this gives the opportunity to test the reaction in special situations 15 PSK Reporter Philip Gladstone N1DQ runs the PSK Reporter system whi
8. TF You can enter a callsign into the field ToCall This is possible only in AutoQSO mode manual Pressing the MOMMAD button or the 2Omfese button will generate the corresponding Standard Procedure for the entered call A Standard Procedure can be deleted by pressing the button only in AutoQSO mode manual The report usually is generated automatically by a double click on a decoded line It can only be altered in AutoQSO mode manual 6 3 Mixed Normal Contest QSOs If a station runs contest mode it sends contest reports Reception of a contest report forces the QSO automatic to reply with a contest report even if it runs in normal mode If a contest station is called with a report it replies with a contest report without roger A manual operator should do the same 6 4 Manual QSOs Set the AutoQSO mode to manual You can select any individual message of the Standard Procedure by clicking the line The SlowPSK program does not accept messages that violate the correct sequence if the AutoQSO mode is not manual Therefore you cannot send RRR before something like RW has been received from the other station At the other end the SlowPSK receiver even will not decode a message which is outside the defined order of the Standard Procedure The manual option only was implemented to cope with computer program rig problems If everything works well then at least the AutoQSO mode QSO should be used because it s operation is more reliable than a
9. and end of the TX and RX periods it is the samplerate which determines the actual length of a packet If the sample rate is correct then the length of a packet is p 996 6 125 s It is shorter if the samplerate is larger If the difference of the samplerates used at both ends of a communication path is so large that the length of the packet sent differs by about one bit or more from what the receiver defines as it s packet length then decoding degrades If the samplerate factors are set correctly then no degradation occurs Use the program samplingrates by DJ5HG to determine the sampling errors The CW ID is sent by keying the SlowPSK signal This is not a clear tone CW signal but the SlowPSK receiver can well decode interrupted signals So the time while the ID is sent is not lost for a QSO You can transmit the CW ID never or at intervals of 1 2 4 or 8 minutes The options of SAVE are none OSO decoded all decoded and all The save audio button in the main GUI is colored audio when the actual recording will be saved All audio recordings are WAV files at sample rate 8000 and mono with 8 bits per sample parameters on green background may be changed in a running QSO Basic Parameters Automatic Operation callsign DJ5HG Stop TX 5 locator JO53IM Stop QSO 20 UTC clock 2 73 4 COM port none PTT none input ID 0 Mikrofo output ID 0 Lautsp input corr 0 9998 output corr 1 0001 CW ID 4min Contest Mode OFF save all decoded QSO
10. ch collects reception reports and displays them according to different options As an example Figure 6 shows a map On 20m v show signals y sent revd by x anyone v g using PSK21 v over the last 24hours v Go Display options Permalink Automatic refresh in 3 minutes Large markers are monitors Display all reports Active PSK21 monitors lt none gt Show all on all bands Show all on all bands Legend lt 9 ta old ra a an as ea i o ED 5 S piae att Niger Be ape OX is Eas i A Congo kenya nn Tanzania gola Nemibis 5 pene Botswana Madagascar Google e System statistics Comments problems etc to Philip Gladstone Online discussion of problems issues Last modified 29 4 2014 13 52 00 Reception records 485 511 228 3 274 PSKREPORTER INFO Figure 6 The PSK Reporter Map SlowPSK can automatically send datagrams with decoded callsigns via the internet to the PSK Reporter The user must explicitely allow this by setting PSK Reporter to ON in the menu bar You also should enter the actual dial frequency into the edit field at the upper right edge of the decoder window in Hz The background of the edit field is gray if the automatic uae 14068000 Br report is set OFF and light green otherwise The reporter goes to OFF if you set the simulator ON by entering some SNR The reporter also goes to OFF if the periodlength is set to more than 1 minute SlowPSK se
11. e at 33 dB 1Z 1Z1Z MM RRR decode not successful Figure 3 A message 3 dB below the sensitivity level could not be synchronized by the 332 address bits blue lines But correlation with the 996 bits of the complete block was successful red lines A new phase recovery based on the new synchronization and a following decode again failed otherwise there would not be the red colored text If correlations are very confident as in this simulation then they can be accepted as received information especially if the same correlation occurs several times in sequence But be careful with peaks of lower height The AutoMode ignores correlations generally by good reasons 3 5 The Operation Parameters Save Save Period AutoQSO EA A EN O 3 5 1 The Save Buttons audio Save the audio signal of the actual receiving period or the last when transmitting graphic Save the actual GraphicalUserInterface as a bitmap file The saved files are stored in the folder records which is located in the same folder as SlowPSK exe and this helpfile SlowPSK_UserGuide pdf 3 5 2 The Period Button Period This is a Selection Button to select one of the displayed options of periods and to select the first or the second period as the TX period The entry Ist 2nd is not relevant in AutoQSO mode reply The receiver then listenes in every period and will aE automatically change this entry if necessary Smin 1st PSK21 with 1 min period i
12. e clipboard A double click on a decoded CQ generates the Standard Procedure SHIFT amp click transfers the Af of the line to the actual FreqOffset which leads to zero beat with that station In the actual case the INWRVENS mode is reply Therefore the reception of line 15 30 in the decoder window triggered the generation of the Standard Procedure and the start of the automatic QSO with the reply transmission RV3APM de DJ5HG rep L 000002 JO53IM 0 5W OdaB The Standard Procedure is automatically cleared by reception of a CQ from the other end Messages received from the same station after the Standard Procedure had been cleared are colored magenta 3 3 The Parameter Buttons FreqOffset FreqTol Fading NoiseBl BirdieBl 3 3 1 FreqOffset This is a toggle button If it is OFF with gray background the frequency offset is 0 i e the output carrier frequency is at the nominal value of 1000 Hz and the expected input carrier is 1000 Hz too and no automatic QSY is made If FreqOffset is set to ON white background color automatic QSY is activated The actual frequency offset is displayed in Hz See Chapter 14 for recommended operation 3 3 2 FreqTol The computational effort of searching for relevant signals is proportional to the search space in frequency This effort can considerably be reduced by setting the frequency tolerance to an acceptable low value FreqTol 20 means that the carrier of the signal to find must be wi
13. e into the clip board A double click on a CQ generates the standard procedure CTRL amp click or right mouse click clears the decoder window 3 2 The Time And Volume Display The actual sound input volume is displayed to the right of the date time display below the decoder window It is colored red if the volume is too high and black if it is too low In the latter case the decoding process stops To the right there is an edit bar to enter messages that shall be searched for by correlation See Chapter 3 4 3 for explanation SlowPSK V1 8 by DJSHG 5 x received information RAZ AL RAZAL RAZ AL LASVNA RAZ AL RV3 APM RV3APM contest mode RV3APM rep RL 000001 KOBERT 5w OdB RV3APM TNX 73 01 Jun 2014 15 35 14 rr FreqTol Fading B BirdieBl To Call acl Generate Standard Mes EE CEE a E E E I EEE a cQ contest de DI5HG RV3APM de DJ5HG RV3APM de DJSHG rep L 000002 3J053IM 0 5w OdB RV3APM de DJSHG rep RL 000002 JO53IM 0 5w OdB RV3APM de DJ5HG RRR Save Save ee Figure 2 The Graphical User Interface GUI of SlowPSK Decoded messages are displayed in the decoder window The lower half of the GUI shows the actual Standard Procedure to the right and signal displays and control buttons to the left This example is from 14068 kHz The GUI can be resized The fonts then are resized too for ex try full screen A single mouse click on a line in the decoder window copies the line into th
14. en CQ QRZ and QST is encoded by two bits Callsigns and general messages are restricted to text of 10 characters of the SlowPSK alphabet They are translated into binary patterns of 54 bits So with the two selection bits we have a total of 56 source information bits The inner code adds 15 check bits for final error detection resulting in 71 bits The channel code encodes the 71 bits by a rate 1 8 convolutional code of constraint length 13 tail ended The resulting codeword has 664 bits As described in 2 4 these bits are interleaved with the general address pattern giving the transmitted block of 996 bits After the receiver recorded a hit with the general address pattern the 664 soft bits are decoded by the Viterbi algorithm resulting in a binary pattern of 71 bits The first 56 bits are used to generate the 15 check bits If any of these generated check bits differs from the received check bits bits 57 71 then the message is discarded The probability to get correct check bits out of wrong received data is 1 32749 To get the rate of displayed false decodes the rate 1 32749 has to be multiplied with the rate of false hits lt 0 01 and with the rate of valid random callsigns 0 001 So the amount of displayed garbage is very small lt 0 0000000003 The codes used in SlowPSK are unmodified linear codes Therefore the all zeroes word is a correct codeword It would decode to QST This special output is caught and n
15. ever displayed It only occurs at random if heavy birdies are present and not blanked out by the birdieblanker 2 6 2 Private Messages Private messages are transmissions addressed to a specific callsign Four message type bits allow 16 different message types within this group including contest messages with QSO number Maidenhead locator etc The information is encoded into 54 bits of source code The 4 message type bits and 13 check bits are added to finally reach 71 bits Other than above the check bits are derived from the concatenation of the 54 source code bits plus the bit pattern of the addressed callsign and plus the bitpattern of the sending callsign if an R or 73 is sent This is important because active callsigns may be very similar Then the address correlation could show hits from similar callsigns These hits are discarded when the check does not succeed The channel code is the same as above 2 7 Automatic Operation Decoded information is immediately discarded if any of the check bits differs As a consequence displayed garbage is extremely rare see Chapter 10 The protection of communicated information is so powerful that a station can run SlowPSK in an automatic mode where SlowPSK automatically replies to incoming calls and runs the QSOs to the final 73 without any interaction by the operator 2 8 Sensitivity 2 8 1 The Block Error Rate of PSK21 The most critical elements in a PSK receiver are 1 the block l
16. for later restauration and try to start SlowPSK again 8 5 SlowPSK_UserGuide pdf This is the document you currently are reading 8 6 records This folder contains all wave files automatically recorded Operating Parameter SAVE or manually taken with the save button audio and all screenshots taken with the save button graphic of the SlowPSK GUI All records are taken mono with samplingrate 8000 and 8 bits per sample The filenames start with SlowPSK_rec followed by the ISO 8601 date in the format yyyymmddTHHMMSS 9 Resuming a QSO after Program Failure SlowPSK is a complex program with many different options It is impossible to test such a program under all situations Several probable problems with the soundcard are eliminated by automatic failure detection and restart But surely many bugs remained undetected If the program fails please try to characterize what had happened If the failure occured within a running and not completed QSO do the following 1 Restart the program 2 Select AutoQSO mode manual 3 Type the callsign of the other station into the field of ToCall 4 Select the same report as before 5 Click the appropriate button OFmal or EOMESH to generate the Standard Procedure messages 6 Select the right message of the Standard Procedure to be sent next Be aware that you are in manual mode now If the QSO traffic is running again in both directions you can select a different AutoQSO mode of your ch
17. go on air in the chosen TX half periods The SlowPSK signal does not have a constant amplitude The TX output power therefore must be adjusted to an SSB level if the PA is peak power limited most solid state PAs 6 Making QSOs 6 1 Starting QSOs There are two ways to get active a Wait for a decoded CQ call in the decoder window A double mouse click on the decoded line will generate all entries of the Standard Procedure and it will automatically select the reply to this CQ as the next transmission If you select the AutoQSO mode QSO or higher the QSO now will run automatically b Start a CQ call by clicking the CQ line in the Standard Procedure If the AutoQSO mode reply is selected replies to your CQ will generate the Standard Procedure automatically and the QSO runs automatically Otherwise the reply only is displayed Here double click on the decoded line to generate the Standard Procedure for the calling station As in 1 the QSO will now run automatically if the AutoQSO mode QSO is selected You can change the AutoQSO mode at any stage of the QSO Select the AutoQSO mode manual if you want to send a special private message edited in the last line of the Standard Procedure section Such a message will only be decoded at the other end if you are in a QSO i e if the other station got a message of line 3 or line 4 of the Standard Procedure and actually runs your call as it s ToCall 6 2 Manual Entry of Callsigns Report and Q
18. human can be 7 The AutoQSO Mode There are five levels of automatic operation The first level manual corresponds to the usual operation of other modes In this level you have to interpret the decoded information of the decoder window by your own to support your decision on which line of the Standard Procedure should be sent next Be careful with your decision because out of order messages will not be decoded at the other end The second level QSO allows the fully automatic operation of the Standard Procedure after a QSO has been started manually The third level reply allows the SlowPSK program to generate and operate the Standard Procedure after a specific call to this station had been recorded It is not necessary to call CQ in this level It is sufficient that some other station starts calling you on the right QRG and with the right period In the fourth level CQ SlowPSK will call CQ whenever it is not in a QSO Replies to the CQ lead to automatic operation of the corresponding Standard Procedures The last level casualCQ is intended for common use of one QRG The CQ is not sent in every TX period but at random with a probability of 20 This results in 6 CQ transmissions per hour in the average If traffik is observed on the QRG then the CQ is blocked for the next 8 minutes Several stations can use this mode at the same time 8 Files All files used and generated by SlowPSK are located in the same folder The location depends on
19. ion is to detect the transmitted packets in time and frequency domain PSK raises a second problem the phase of the received signal must be determined from this signal SlowPSK interleaves the 664 bits of codewords with a binary address pattern of 332 bits such that every 3rd bit of a block bits 1 4 7 10 991 994 is known to the addressed receiver These bits are used for phase recovery and for block detection There are two types of addresses 1 a specific binary pattern of 332 bits used as a general broadcast address for CQ QRZ QST and 2 a unique binary pattern for each callsign 2 6 Code Formats In all cases three nested codes are used The outer convolutional code the channel code is for error correction The inner code is for detection of remaining errors It is mainly this code that prevents from display of garbage The third code is the source code which translates the bit arrays into displayed text output There is a plausibility check at this stage which refuses the display of callsigns that do not comply with the syntax of callsigns 99 9 of random texts are invalid There are several coding schemes for different message types Here only a brief overview is given For details see the SlowPSK documentation 2 6 1 General Messages CQ QRZ QST These three messages communicate a callsign of up to 10 characters in case of CQ or QRZ or some general message of 10 characters in case of a QST The selection betwe
20. lowPSK again PSK Spectrum opens a new window which shows possible locations of BPSK signals over the frequency range 1500 df FreqTol 1500 df FreqTol The displayed information is similar to a spectrum It is a nonlinear combination of three sources 1 the original spectrum 2 the spectrum filtered by a matched filter and 3 the spectrum of the squared signal PSK Reporter is discussed in Chapter 15 Simulation is discussed in Chapter 13 4 The Parameter GUI Some basic parameters are set via a parameter GUI It is shown in Figure 4 If this GUI is not already open then select options in the menu bar of the main GUI 4 1 Basic Parameters Here enter your actual callsign possibly including guest prefix or P etc The maximum length of the callsign is 10 characters The locator is the full Maidenhead locator UTC clock means UTC minus computer clock in hours So it is negative if you live at least one hour east from Greenwich You can select the COM port for TRX control with the COM port parameter The PTT parameter offers the choice of the DTR or the RTS lines choose DTR or RTS for inverted levels There are pulldown menues for the soundcard IDs for both input and output These IDs are not the same as in other programs which use the soundcard You have to try it out The samplerate correction factors input corr and output corr must be set as precisely as possible While the PC clock determines the start
21. nd the other runs normal mode then the other station automatically is enforced to run the QSO in contest mode too The QSO number for the next QSO can be set here It is incremented automatically So you need not to enter it every QSO Power and Antenna Gain can be selected for the contest format These values should be set in any case because a call could enforce you to run in contest mode 5 Checking the Interaction of SlowPSK with the TRX Hardware 5 1 Parameters Set the parameters in the Parameter GUI according to the previous Chapter 4 Choose the right soundcard ID and set the AutoMode to manual 5 2 Computer Clock Check the computer clock The difference to the UTC minutes should be much less than the value chosen for TimeTol 5 3 Test Received Audio Switch your rig ON and adjust the volume such that the value of the input volume display in the SlowPSK GUI is between 10 dB and 10 dB letters not black or red 5 4 Test Signal Output Connect your earphones to the selected sound output of your computer Choose the period to 1min Ist or Imin 2nd Click on the standard message QRZ de YourCall Then check whether SlowPSK switches the output signal ON when the selected line of the Standard Procedure is switched to yellow color 5 5 Test TRX Control Connect the PTT of your TRX with the RS 232 interface Choose the appropriate values for COM port and PTT in the Parameter Gui Now repeat the test 5 4 The TX should
22. ndard Procedure of a QSO is XYZ AB1CDE v normal contest controlled by three colored buttons ST normal pushing this button i generates the last 6 lines of the Standard Procedure for a normal QSO pushing this button generates the last 6 lines of the Standard Procedure for a contest QSO The CQ de DI5HG QRZ de DISHG XYZ ABLCDE de DJ5HG XYZ AB1CDE de DJ5HG rep Ww 000017 3053IM 100w 15dB XYZ ABLCDE de DJ5HG rep RW 000017 3053IM 100w 15dB XYZ AB1CDE de DJ5HG RRR XYZ ABLCDE de DJ5HG TNX 73 QSO nuiib er is updated XYZ AB1CDE de DJ5HG automatically clears the entry of ToCall and the last 6 lines of the Standard Procedure The ToCall can be entered manually into the edit field A double click on a decoded CQ call in the decoder window will set ToCall and generate the Standard Procedure If this is done while a QSO is running a non modal warndialog demands for a user decision between abort the running QSO or do not start a new QSO 3 6 The Menu Bar The menu bar is self explaining The file Exit option of the menu guarantees a clean exit from SlowPSK but it may take a while because it stops all concurrent processes in an ordered sequence Options basic parameters opens a GUI to set basic parameters see next Chapter Options save GUI position saves the actual size and location of the SlowPSK window Options default GUI position restores the default position of the SlowPSK window Exit and start S
23. nds the following information via the internet 1 The receiver information example your callsign DJS5HG your locator JO53IM your actual decoding software SlowPSK V2 0 the entries of the contest parameters for antenna and power vertical SW 2 The reception reports frequency 14068000 mode PSK21 UTC of decode 25 Jun 2014 21 37 29 decoded callsign UAOSNV SNR 30 SlowPSK sends this information with the datagram protocol This is a one way communication To get the information back you have to open https pskreporter info pskmap html or something else
24. not be decoded within a QSO the possible blocks are generated and correlated with the received signal If this leads to significant peaks in time and frequency the phase synchronization is based on this correlation and a digital decode is tried again If that results in a decode the printed textline is marked by an asterisk If it fails the synchronization is displayed in red color and the corresponding message is printed into the time synchronization display The message does not show up then in the decoder window because there is no error correction and no error detection By this reason it is never used in an automatic QSO Nevertheless it surely is interesting for the operator to know how many dBs the received signal is below the decoder level Figure 3 gives an example In a manual QSO the correlation may be used if the peaks in both displays are very significant at least as good as in Figure 3 The information corresponds to the short messages of JT65 But SlowPSK includes the report and there will be no correlation if a callsign is wrong 3 4 3 Correlation with a Known Message SlowPSK also can correlate with non QSO messages There is a text entry see 3 2 for such messages These messages must not contain a report The callsigns may be arbitrary up to 10 characters each If this text field is not empty the correlation is tried only after the decoder failed and the correlation with expected QSO messages did not succeed messag
25. number 1 carrier normal TX power 10W samplerate normal Ant Gain 0dB Contest Parameters Figure 4 Window with standard parameters Some parameters may be entered as an editable text callsign and QSO number for example others may be selected in a pulldown menu Parameters shown on light green backgroud may be changed within a running QSO The carrier option only should be changed to 1500 Hz if you want to use a TRX narrow band filter which works with center frequency 1500 Hz and not with 1000 Hz and PBT cannot shift it there If 1500 is selected then the dial frequency of the TXR must be 500 Hz lower than in the normal case Carrier may be changed at any time The samplerate option of 48000 is for use with SDR Please avoid this option if possible It costs about a million floatingpoint operations per second extra 4 2 Parameters for Automatic Operation STOP TX sets the maximum number of TX periods for the same message This timeout only is activated in automatic operation STOP QSO sets the maximum number of TX periods of a QSO This timeout only is activated in automatic operation 73 sets the number of periods you want to send the 73 message after having received the final RRR It is convenient to send 73 or CQ to inform the other end that the QSO is complete 4 3 Contest Parameters If Contest Mode is set to ON then a QSO is started by a call of the other station without report If one station runs contest mode a
26. ocalization in frequency and time and 2 the phase recovery If the radio channel severely distorts the signal phase then the rate of failure of the phase recovery is high at marginal conditions The utmost sensitivity only is reached if there is no or very slow fading Medium fading causes a loss of 2 dB fast fading gt 20 minima in period even leads to a loss of 4 dB See Chapter 12 for more information The block error rates were determined with a channel simulator The results for PSK21 are given in Figure 1 Block Error Rate of PSK21 block error rate GPS sync no fading r medium fading fast fading confident correlation 10 I I I I jt i i i i 38 37 36 35 34 33 32 31 30 29 SNR in bandwidth 2500 Hz dB i i i j 28 27 26 25 24 Figure 1 Block error rate of PSK21 as a function of the SNR in a bandwidth of 2500 Hz GPS sync means frequency error lt 0 1 Hz and time error lt 0 5 s otherwise frequency error lt 10 Hz and time error lt 2 s solid lines successful digital decode dashed line confident detection of an expected message by correlation Compared to the phase distortion additive non Gaussian noise like birdies or spikes from electrical machines can hardly jam a PSK reception if the receiver uses a noise blanker and a birdie blanker 100 pulses of 1000 times the amplitude of the signal occurring within one period lead to a
27. oice for example QSO 10 The Rate of False Decodes SlowPSK only tries to decode a received signal when there is a significant correlation with one of the two addresses The rate of significant false correlations c is not negligible Without the error detecting code the second code of SlowPSK there would be a considerable amount of false decodes and that would render the AutoQSO mode impossible But SlowPSK uses the error detecting residual code of r 15 13 bits in CQ calls QSO messages That reduces the rate of false decodes down to about c 2 lt 0 00001 Even in the fastest submode with period of 1 minute this is no more than one false decode per month of continuous operation The correlation with QSO messages and messages entered into the Correlate entry may display false results because there is no no error correction and no error detection These displayed results with the exception of the SNR are not information which has been received via the radio waves 10 1 Non Fatal False Decodes The most probable false decodes are of the type TOCALL de MYCALL free text of 10 characters In the automode they have no relevance In manual mode such messages also have no relevance because it is extremely improbable that they display senseful text Also false QSTs like QST L 7NCD6ADRF can occur QSTs are messages to all operators They do not carry any QSO information and they are simply displayed by the SlowPSK program without notice
28. ple noise blanker NB can be switched ON and OFF It is a powerful tool for reading signals in pulse like non Gaussian noise In absence of pulse noise the NB should be set to OFF 3 3 5 BirdieBl A simple birdie blanker BB can be switched ON and OFF It is a powerful tool for finding and reading signals in birdie like non Gaussian noise Since the SlowPSK signal does not show a carrier in the input signal it is not cleared by the BB Therefore weak signals can be identified and decoded even if strong birdies are present In absence of birdies the BB should be set to OFF 3 4 The Sychronization Displays 3 4 1 The Normal Display The output of the synchronization in time relative to the expected value within the allowed time interval 6 s 6 s is diplayed on the left side The corresponding synchronization within the frequency interval 2 Hz 2 Hz is displayed on the right side Peaks within the gray background are not confident The confidence is given by the vertical scale The peak height 21 of the TimeSync means that pure Gaussian noise will generate such a peak once in 10 periods Therefore this peak of a signal at 28 dB is very confident 3 4 2 Correlation with Expected QSO Messages If you are in a normal QSO then the number of possible messages expected to be received from the other end depends on the actual QSO state It is 3 if it should contain a report or 1 if you are waiting for RRR or 73 If a received period can
29. s not for EME operation There is a special version Smin 2nd EMEPSK The difference between EMEPSK and SlowPSK with the selection 15min 1st Imin is that in EMEPSK both the TX frequency and the RX frequency are 15min2nd corrected for Doppler shift caused by the motion of the Moon and by the Earth s rotation such that the frequencies do not show any Doppler at the Moon s center min zn 3 5 3 The AutoQSO Button There are five different modes of automatic operation manual means that operation has to de done manually QSO means that the SlowPSK program will run the Standard Procedure automatically after the user had started a QSO manually reply means that SlowPSK will automatically start and finish a QSO if it casualCQ records a call to this station CQ means that this station will automatically call CQ after a QSO has been finished The further behaviour is as in mode reply casualCQ this does the same as CQ but in every TX period a random generator decides upon the actual transmission of the CQ at a rate of 20 If traffik is detected on the QRG the CQ is blocked for the next 8 minutes 3 5 4 The StopTX Button This Button is colored with red background if the TX is transmitting see Figure 2 Pushing the button then immediately will stop the TX The TX can be switched to ON again by a click into the corresponding line of the Standard Procedure 3 6 The Standard Procedure To Call Me cicecucciehccctescmm The Sta
30. thin 20 Hz of the nominal carrier frequency 1000 Hz The sensitivity decreases with FreqTol gt 2 The background of the FreqTol button then is colored pink Large values 100 200 are for search of signals The search is sensitive to any BPSK signal Therefore care must be taken in using a value as large as 200 because a PSK31 signal may be selected as the biggest one while a weaker SlowPSK signal then is ignored If automatic QSY is activated gray background on the FreqOffset button then the frequency offset is adapted to the first received signal of the other station in a QSO and FreqTol is set to an appropriate low value The frequency offset is set to 0 and the previous value of FreqTol restored when a QSO ends 3 3 3 Fading The carrier phase of a received block is modelled by a complex polynomial of degree d This polynomial therefore has 2 d 1 real parameters which have to be derived from the signal additionally to the binary information Since the information content of the signal is limited by the noise choosing a large value of d leads to a better phase recovery but it increases the noise in the demodulated signal By this reason the polynomial degree should be adapted to the properties of the actual radio channel SlowPSK therefore offers the following options also see Chapter 12 selection degree maximum number of fading minima no fading 6 1 medium fading 30 7 fast fading 80 20 flutter 200 50 3 3 4 NoiseBl A sim
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